AU2005229725B2

AU2005229725B2 - Dust extraction for power tools

Info

Publication number: AU2005229725B2
Application number: AU2005229725A
Authority: AU
Inventors: Andrew Walker
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 2004-11-19
Filing date: 2005-11-04
Publication date: 2010-04-22
Anticipated expiration: 2025-11-04
Also published as: ES2298670T3; ATE385213T1; DE602004011624D1; CA2517944C; EP1661661B1; US20060107633A1; EP1661661A1; CN1775485A; DE602004011624T2; AU2005229725A1; US7497886B2; CN100482424C; CA2517944A1

Abstract

There is provided a power tool (30) comprising: a working head (32) for holding a working element; a duct (40) having an inlet locatable in proximity to a point of contact between the working element and a workpiece; a dust collection chamber (50) having an inlet (52) in fluid communication with an outlet (44) from said duct, and an outlet (54) in fluid communication with atmospheric air; a fan (70) operable to transport air from the inlet of said duct to the outlet (44) thereof; and a filter (60) located in fluid flow between the outlet (54) of said dust collection chamber and atmospheric air; wherein the dust collection chamber (50) has a substantially circular cross section, the inlet (52) to said dust collection chamber is at the perimeter of said circle and the outlet (54) of said dust collection chamber is from the middle of said circle. There is also provided a dust extraction module for use with a power tool, said dust extraction module comprising: a dust collection chamber (50) having an inlet (52) connectable in fluid communication with an outlet (44) of a dust-extracting duct (40) of said power tool, and having an outlet (54) in fluid communication with atmospheric air; and a filter (60) locatable in fluid flow between the outlet of said dust collection chamber and said atmospheric air; wherein the dust collection chamber (50) has a substantially circular cross section, the inlet (52) to said dust collection chamber is at the perimeter of said circle and the outlet (54) of said dust collection chamber is from the middle of said circle.

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S):: Black & Decker Inc ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Nicholson Street, Melbourne, 3000, Australia INVENTION TITLE: Dust extraction for power tools The following statement is a full description of this invention, including the best method of performing it known to me/us: 5102 la The present invention relates to dust extraction for power tools. The invention has particular, though not necessarily exclusive, application to dust extraction for power tools of the hand-holdable variety, such as sanders, drills, 5 routers, saws, hammers, grinders and the like. Typically, these power tools generate sawdust when applied to a workpiece made of wood. The dust generated when such tools are used is of a fine particulate nature and floats easily into surrounding air under normal operating conditions. Vibrations 10 associated with the operation of said tools also tends to disperse this dust still further. A working environment containing suspended dust is unpleasant, inconvenient and may even be unhealthy for users of these tools. Moreover, once the dust has settled, a clean-up operation is also required to remove the scattered dust from the environment. In view of these problems, a number of prior art arrangements have 15 already been developed for extracting dust from around the operating region of power tools. Early ideas for dust extraction systems are discussed in two sections headed "Dust Extraction Systems" and "Dust Separation Units" on pages 104-116 of the book 20 "Ergonomic Tools in our Time", an Atlas-Copco publication, by Bo Lindqvist et al., 1986 (ISBN: 91 7810 535 8). This account of dust extraction breaks the dust extraction process down into a chain of components as shown in Fig.1. From the point of creation of the dust 100, these are as follows: a dust extraction hood 200 located close to the point where the dust is generated, a suction hose 300 connected 25 to the dust extraction hood, a swing arm 400 for supporting the suction hose, suitable pipework 500 connecting the suction hose with some means 600 for separating the dust from air taken in by the dust extraction system and a vacuum source 700 for generating a flow of air through the dust extraction system. Examples which are given of the means for separating the dust from air taken in by the dust extraction 30 system include cyclones and filters, and examples which are given of the vacuum source for generating a flow of air through the dust extraction system include fans and root pumps. In all of the account given in this book, however, it can be seen that although the power tools which are under consideration are hand-holdable tools, the 2 dust extraction system which is intended for use in association with them is far from being hand-holdable and is a much larger, permanently mounted system. Examples of some more recent ideas for dust extraction techniques for use 5 with hand-holdable power tools which are themselves also highly portable concentrate on the idea of using the same motor which provides power to the tool itself for its main function also being used as the source of power for generating a flow of air through the dust extraction system. In comparison to the system shown in Fig. 1, therefore, this allows a considerable saving on space and weight. Since the 10 motor which provides power to the tool's main function also acts as the source of power for generating a flow of air through the dust extraction system, there is no need to locate the means for separating the dust from air taken in by the dust extraction system at a distance which is remote from the region where the dust is generated, namely the point of contact between a working element (such as a drill 15 bit, saw blade, sheet of sandpaper, or the like) which is held by a working head of the power tool, and a workpiece, such as a piece of wood. Consequently, there is also no need for a suction hose or other pipework to connect the region where dust is generated with the means for separating the dust from air taken in by the dust extraction system. Instead, a short duct built into the power tool itself will generally 20 suffice. Accordingly, these dust extraction systems generally comprise a duct having an inlet locatable in proximity to the point of contact between the working element held by the power tool and a workpiece, a dust collection chamber having an inlet in fluid communication with an outlet from said duct, and an outlet in fluid communication with atmospheric air, a fan operable to transport air from the inlet of 25 said duct to the outlet thereof, and a filter located in fluid flow between the outlet of said dust collection chamber and atmospheric air. A first example of such a dust extraction system is described in US patent no. 6,514,131 assigned to Robert Bosch GmbH. This patent shows a sander having a 30 platten (labelled 16 in US 6,514,131) for holding a sheet of sandpaper, a fan (labelled 19) for transporting air from the point of contact between the sandpaper and a workpiece through a duct to an outlet 20 thereof, which exhausts into a dust collection chamber 21. The dust collection chamber 21 is a rigid, self-supporting box having a cover 23 with a plurality of openings 40 in fluid communication with P-AU-CS1217 3 atmospheric air. Located in fluid flow between these openings 40 and atmospheric air is a filter element 48 which extracts dust from the air passing to atmosphere, causing it to be held in the dust collection chamber 21. 5 A second example of such a dust extraction system is described in US patent no. 6,224,471 assigned to Porter Cable Corporation. This patent also shows a sander, which has a platten (labelled 22 in US 6,224,471) for holding a sheet of sandpaper, a fan with blades (labelled 37 therein) for transporting air from the point of contact between the sandpaper and a workpiece through a duct 58 into a dust 10 collection chamber 60. In this case, the dust collection chamber 60 is formed from a porous plastic material, so that the interior of the dust collection chamber is in fluid communication with atmospheric air and the body of the chamber 60 itself acts as a filter for extracting dust which is collected therein. A membrane 62 formed across the inlet to the dust collection chamber acts as a trapdoor to prevent dust returning down 15 duct 58 under the action of gravity when the fan is switched off. In US patent no. 6,224,471, the dust collection chamber is substantially cylindrical in shape and therefore has a substantially circular cross-section, and the inlet thereto is located on one of the end faces of the cylinder, with the curved surface of the cylinder and the other end face thereof acting as the outlet. 20 A further example is described in US patent no. 4,967,516 assigned to Ryobi Motor Products Corporation. This patent also describes a sander having a platten 18 for holding a sheet of sandpaper, a fan 36 for transporting air from the point of contact between the sandpaper and a workpiece through a duct 70 having an outlet 25 72 which exhausts into a dust collection chamber 74. In this case, the dust collection chamber is a semi-rigid frame having a plurality of windows formed therein in fluid communication with atmospheric air. Each of the windows is covered by a mesh fabric which extracts dust from the air passing to atmosphere, causing it to be held in the dust collection chamber 74. 30 A final example of a known dust extraction system for use which a power tool is shown in Fig. 2. Here, a drill 10, having a working head (chuck) 12 for holding a drill bit, is provided with a dust collection chamber 14, which is connected via a duct 16 with a fan housed in drill 12. The duct 16 is provided with an inlet 18 locatable in P-AU-CS1217 4 proximity to a point of contact between the drill held by chuck 12 and a workpiece. The dust collection chamber 14 contains a fabric bag 20 as shown in Fig. 3. In turn, the fabric bag 20 itself contains a plastic frame 22, which comprises a centrally located tube 24 open at both ends and having a mouth 26, as shown in Fig. 4, where 5 the frame 22 has been removed from bag 20 to show its construction. The inlet 18 to duct 16 is so arranged that during operation of the fan, dust-laden air passes through the mouth 26 of tube 24 in the direction indicated by arrow A in Fig. 4 into the interior of bag 20 in the direction indicated by arrow B in Fig. 4 where the dust is collected. Filtered air then passes outwards through the bag 20 into dust collection chamber 14 10 and thence down duct 16 to the fan housed in drill 12, where it is exhausted to atmosphere through the vents 28 shown in Fig. 2. Thus, this prior art dust extraction system is distinguished from those disclosed in US 6,514,131, US 6,224,471 and US 4,967,516 in that it uses a "clean fan", rather than "dirty fan" dust extraction technique. In other words, in this system, the air transported by the fan is filtered 15 before it makes contact with the fan, rather than after. In this respect, the dust extraction system described in relation to Figs. 2 to 4 is analogous in both the layout of its components and its mode of operation to a conventional domestic vacuum cleaner. 20 However, all of the prior art dust collection systems shown in US 6,514,131, US 6,224,471 and US 4,967,516 and in Figs. 2 to 4 below suffer from the disadvantage that the filters used therein easily become blocked with dust, thereby rapidly diminishing the performance of these dust extraction systems. Moreover, unlike the dust extraction system discussed above in relation to Fig. 1, since the motor which 25 powers the fan for transporting air through these dust extraction systems also provides motive power to the working head of the power tool, if the filters therein do become clogged with dust, the operation of the fan cannot be increased by a similar amout to compensate. 30 In a first aspect, the present invention provides a power tool comprising: a working head for holding a working element; a duct having an inlet locatable in proximity to a point of contact between the working element and a workpiece; a dust collection chamber having an inlet in fluid communication with an outlet from said duct, and an outlet in fluid communication with atmospheric air; a fan operable to 5 transport air from the inlet of said duct to the outlet thereof; and a filter located in fluid flow between the outlet of said dust collection chamber and atmospheric air, wherein the dust collection chamber has a substantially circular cross section, the inlet to said dust collection chamber is at the perimeter of said circle and the outlet of said dust 5 collection chamber is from the middle of said circle. In a second aspect, the present invention also provides a dust extraction module for use with a power tool, said dust extraction module comprising: a dust collection chamber having an inlet connectable in fluid communication with an outlet 10 of a dust-extracting duct of said power tool, and having an outlet in fluid communication with atmospheric air; and a filter locatable in fluid flow between the outlet of said dust collection chamber and said atmospheric air; wherein the dust collection chamber has a substantially circular cross section, the inlet to said dust collection chamber is at the perimeter of said circle and the outlet of said dust 15 collection chamber is from the middle of said circle. Preferred embodiments of the present invention provide a solution to technical problems with the types of dust extraction systems described in US 6,514,131, US 6,224,471 and US 4,967,516 and in relation to Figs. 2 to 4 below, without 20 engendering the problems with the alternative dust extraction system described above in relation to Fig. 1. In each of these two aspects of the present invention, the dust collection chamber has a substantially circular cross section, the inlet to said dust collection 25 chamber is at the perimeter of said circle and the outlet of said dust collection chamber is from the middle of said circle. With this arrangement, dust-laden air entering the dust collection chamber may be caused to swirl around in a circular manner and flung against the outer wall of the dust collection chamber under the action of centrifugal force before air is exhausted from the dust collection chamber 30 through the filter to atmosphere. Thus the air encountering the filter can be less dust laden than if the air encountered the filter directly. The throughput of air through the dust extraction system and the performance thereof may be accordingly enhanced, and the filter not subject to clogging as rapidly as the prior art systems described 6 above in US 6,514,131, US 6,224,471 and US 4,967,516 and in relation to Figs. 2 to 4 below. A dust extraction system in a power tool embodying the invention uses "dirty 5 fan" operation, wherein the dust-laden air encounters the fan before it is filtered, whereby it does not have the disadvantages of the dust extraction system described in relation to Fig. 1, wherein the vacuum source 700, which performs the same function as the fan in the preferred embodiments of the invention, is located after the separation means 600, where the dust is extracted. 10 Moreover, whereas in US patent no. 6,224,471, the dust collection chamber is substantially cylindrical in shape and therefore has a substantially circular cross section, the inlet thereto is located on one of the end faces of the cylinder, with the curved surface of the cylinder and the other end face thereof acting as the outlet, in 15 contrast to the power tool or dust extraction module of the present invention, wherein the inlet to the dust collection chamber is at the perimeter of said circle and the outlet of said dust collection chamber is from the middle of thereof, and accordingly lacks the beneficial technical effects described above. 20 In a preferred embodiment of the present invention, the cross-sectional area of the inlet to the dust collection chamber is greater than or equal to the cross-sectional area of the inlet to the duct and/or the cross-sectional area of the outlet from the dust collection chamber is greater than or equal to the cross-sectional area of the inlet thereto and/or the cross-sectional area of the outlet from the dust collection chamber 25 is greater than or equal to the cross-sectional area of the inlet to the duct. Thus in the most preferred of these alternatives where all three conditions are true, the cross sectional area of the pathway of the dust-laden air from the point of contact between the working element and the workpiece to atmospheric air always increases. This helps to increase the throughput of the dust extraction system and counters the 30 effects of filter clogging still further. In another preferred embodiment, the inlet to the dust collection chamber is located above a horizontal plane having at least two-thirds of the interior volume of the dust collection chamber above the plane. This ensures that dust collected in the 7 dust collection chamber is held therein and cannot fall back down the duct under the action of gravity when the fan is switched off. The higher the inlet to the dust collection chamber is located above the horizontal plane, the greater the amount of dust which can be held in the dust collection chamber and the better the effect 5 achieved. In another preferred embodiment, the exterior of the dust collection chamber is substantially symmetrical about a vertical plane containing the longitudinal axis of the power tool, allowing the power tool to be used by a left- or by a right-handed person 10 without the appendage of the dust collection chamber providing an obstruction preventing the power tool from being held with comfort. In such a case, if the dust collection chamber is detachable from the power tool, the outlet of the duct and the inlet to the dust collection chamber can have complementary asymmetric profiles, to ensure that the dust collection chamber is attachable to the outlet of the duct in only 15 one possible configuration. Thus although the dust collection chamber is apparently symmetrical from outside, it cannot be fitted to the power tool upside-down, which might undesirably place the inlet to the dust collection chamber below a horizontal plane having at least two-thirds of the interior volume of the dust collection chamber above that plane. However, this option may also be used even if the dust collection 20 chamber is not substantially symmetrical to ensure its correct fitment. In a further preferred embodiment adapted to allow for equally comfortable use of the power tool by both left- and right-handed users, the exterior of the dust collection chamber may be asymmetric about a vertical plane containing the 25 longitudinal axis of the power tool, with the dust collection chamber detachable from the power tool, and the dust collection chamber attachable to the outlet of the duct in two possible alternative configurations, one configuration being for use of the power tool by a left-handed person, and the other configuration being for use of the power tool by a right-handed person. 30 Conveniently, the duct may be contained within a handle of the power tool, thereby saving space and materials during manufacture. P-AU-CS1217 8 Since the dust extraction technique is liable to generate a build-up of static electricity in the dust collection chamber, in a preferred embodiment, the dust collection chamber is provided with an anti-static or conductive coating, or with an earthing wire, thereby mitigating this effect. 5 The dust collection chamber may also be made at least partially transparent to allow a user to see how full it is and when it needs emptying. In such a case, the transparent parts of the dust collection chamber are preferably made of polypropylene, which is found to be a good material for resisting the effects of static 10 build-up just described. The dust collection chamber may also be at least partially made of glass-filled nylon, which has a similar beneficial property. Preferably, the dust collection chamber comprises a door or lid, which allows a user to empty it. In a preferred embodiment, the filter is removable from the dust 15 collection chamber and replaceable, which also allows a user to clean it and replace it or to discard it completely and replace it with a new filter. The filter may be of any conventional type, such as a fabric filter, a pleated filter or a mesh. The filter may also comprise a first filter element for filtering course dust 20 and a second filter element for filtering finer dust than the first filter element, or further additional stages of filtration to improve performance still further. In a preferred embodiment, the dust collection chamber is substantially in the shape of a cylinder having a longitudinal axis oriented substantially horizontally with 25 respect to the power tool, the inlet to said dust collection chamber is located on the curved surface of said cylinder, and the outlet of said dust collection chamber is located on an end face of said cylinder. Thus in this preferred configuration, the dust collection chamber may be arranged in an ergonomically desirable position on the power tool with the outlet of the dust collection chamber venting to atmospheric air in 30 a substantially horizontal direction away from a user for maximum comfort. In an alternative preferred embodiment, the dust collection chamber is substantially in the shape of a drum having an axis of rotational symmetry oriented substantially vertically with respect to the power tool, the inlet to said dust collection 9 chamber is located on the curved surface of said drum, and the outlet of said dust collection chamber is located on the upper face of said drum. Thus in this preferred configuration, the dust collection chamber may be arranged in an ergonomically desirable position on the power tool with the outlet of the dust collection chamber 5 venting to atmospheric air in a substantially vertical direction away from the surface of the workpiece, in order to avoid disturbing dust being created at the point of contact between a working element being held by the power tool and the workpiece. In either case, the filter may be located centrally within the dust collection 10 chamber coaxially with said axis of the dust collection chamber. This has the advantage of keeping the filter away from the parts of the dust collection chamber where the airspeed of the dust-laden air is greatest, thereby minimizing the chance of the filter becoming blocked and improving performance. 15 Preferably, if the dust collection chamber is substantially in the shape of a cylinder, it may contain a second smaller cylinder, the second smaller cylinder having the same orientation as and being coaxial with the first said cylinder, the second cylinder being open at one end thereof to the interior of the dust collection chamber and at the other end thereof providing the outlet from the dust collection chamber, 20 with the filter located across or around said outlet. Alternatively, if the dust collection chamber is substantially in the shape of a drum, it may contain a second smaller drum, the second smaller drum having the same orientation as and being coaxial with the first said drum, the second drum being open on the lower face thereof to the interior of the dust collection chamber and on the upper face thereof providing the 25 outlet from the dust collection chamber, with the filter located across or around said outlet. In both of these cases, the performance of the dust extraction is improved because the second smaller cylinder or drum helps to keep dust away from the filter, thereby reducing clogging still futher. 30 In common with the prior art dust extraction systems described in US 6,514,131, US 6,224,471 and US 4,967,516, the fan is preferably located on a drive shaft of a motor of the power tool, which motor also provides the motive power for the working head of the power tool, thereby giving the same advantages of compactness and low overall weight as these prior art systems. Moreover, the same drive shaft P-AU-CS1217 10 may carry a second fan operable to cool the motor. However, in such a case it is desirable that the second fan is contained in a chamber of the power tool which is sealed from fluid communication with the duct forming part of the dust extraction system. This ensures that dust-laden air is not used to cool the motor, which would 5 be undesirable and likely to damage the motor. A dust collection module embodying the invention may be adapted to fit more than one different power tool, in order to allow it to be interchanged between power tools. 10 Further features and advantages of the present invention will become apparent from the followed detailed description, given in association with the accompanying drawings, wherein: 15 Fig. 1 is a schematic representation of a first prior art dust extraction system; Fig. 2 shows a second prior art dust extraction system used with a drill; Fig. 3 shows the dust collection chamber and filter bag of the dust extraction system of Fig. 2 in a disassembled state; Fig. 4 shows the dust collection chamber and filter bag of the dust extraction 20 system of Fig. 2 further disassembled to show a plastic frame contained in said bag during operation of the dust extraction system; Fig 5 is a side view of a power tool which is a first embodiment of the present invention; Fig. 6 is a perspective view of the power tool shown in Fig 5; 25 Fig. 7 is an exploded view of the same embodiment as shown in Figs. 5 and 6; Fig. 8 is a more detailed view of the dust collection chamber of the embodiment of Figs. 5 to 7; Fig. 9 is an exploded view of the same dust collection chamber shown in Fig. 8; Fig. 10 is a general view of power tools according to second, third and fourth 30 embodiments of the invention; Fig. 11 is a perspective view of the second embodiment of the invention; Fig. 12A is a partially cut-away view of the power tool according to the second embodiment of the invention seen from one side thereof; 11 Fig. 12B is a partially cut-away view of the power tool according to the second embodiment of the invention seen from the rear thereof; Fig. 13 is a perspective view of the third embodiment of the invention; Fig. 14 is a partially cut-away view of the power tool according to the third 5 embodiment of the invention seen from one side thereof; Fig. 15 is a perspective view of the fourth embodiment of the invention; and Fig. 16 is a partially cut-away view of the power tool according to the fourth embodiment of the invention seen from one side thereof. 10 Referring firstly to Figs. 5 and 6, there is shown a power tool 30, which in this embodiment is a sander, having a working head 32, here a platten, for holding a working element, namely a sheet of sandpaper. A duct 40 has an inlet locatable in close proximity to the point of contact between the sheet of sandpaper and a workpiece by the provision of through-holes formed in the platten 32 in a 15 conventional manner. A dust collection chamber 50 has an inlet 52 in fluid communication with an outlet from said duct, and an outlet 54 in fluid communication with atmospheric air. In this embodiment, the dust collection chamber 50 is substantially in the shape of a cylinder having a longitudinal axis oriented substantially horizontally with respect to the power tool, the inlet 52 to the dust 20 collection chamber is located on the curved surface of the cylinder, and the outlet 54 of the dust collection chamber is located on an end face of the cylinder. Fig. 7 shows an exploded view of the same embodiment as shown in Figs. 5 and 6, where the dust collection chamber 50 has been detached from the duct 40. 25 This shows the manner of connection of the inlet 52 of the dust collection chamber 50 to the outlet 44 of the duct 40, and in particular that outlet 46 is provided with a groove 46 which is offset to one side of a vertical plane containing the longitudinal axis of the power tool 30. Groove 46 has a complementary profile to a ridge not visible in Fig. 7 provided on the interior of inlet 52, so that the dust collection 30 chamber 50 is only attachable to the outlet of the duct 40 in one possible configuration, namely that shown in Fig. 6. This prevents the dust collection chamber 50 from being attached to the outlet 44 upside down. P-AU CS1217 12 The cross-sectional area of the outlet 54 of the dust collection chamber 50 is also greater than the cross-sectional area of inlet 52, which is in turn itself larger than the combined cross-sectional area of the through-holes formed in platten 32. Thus the cross-sectional area of the pathway for dust-laden air from the platten to 5 atmospheric air always increases and the throughput of the dust extraction system is thereby also improved. Fig. 8 is a more detailed view of the dust collection chamber 50 of this embodiment. As may be seen from Fig. 8, the interior of the outlet 54 of the dust collection chamber reveals a pleated filter 60, having a generally cylindrical shape. 10 This is more readily visible in Fig. 9, which is an exploded view of the same dust collection chamber shown in Fig. 8. Here, it can be seen that the filter 60 comprises a pleated filter element 601 shaped into the curved surface of a cylinder and a blank wall 602 which forms one of the end faces of said cylinder. The other end face thereof is open to the outlet 54 of the dust collection chamber, as shown in Fig. 8. 15 Fig. 9 also shows that the dust collection chamber 50 comprises a lid 501 and a body portion 502, which allows the dust collection chamber 50 to be opened by a user and emptied. Body portion 502 is transparent, allowing a user to see the level of dust collected in the chamber and therefore when it needs emptying. Moreover, 20 filter 60 is removable from the dust collection chamber 50 and replacable, which also allows a user to clean it and replace it or to discard it completely and replace it with a new filter. Finally, Fig. 9 further shows the method of attachment of lid 501 to body portion 25 502 of the dust collection chamber 50. Body portion 502 is provided on opposite sides of the rim thereof with a pair of lugs 503, one of which can be seen in Fig. 9. Lugs 503 engage with a pair of corresponding tracks 504 formed in lid 501, one of which tracks 504 can also be seen in Fig.9. 30 Fig. 10 is a general view of second, third and fourth embodiments of the invention, showing three power tools labelled 301, 302 and 303. 301 is a quarter-sheet sander, 302 is a random-orbit sander and 303 is a belt sander. All are provided with dust extraction systems. As can be seen from Fig. 10, the dust collection chambers of sanders 301 and 303 are 13 generally in the shape of a cylinder having its longitudinal axis oriented substantially horizontally with respect to the sander, with the inlet to the dust collection chamber located in both cases on the curved surface of the cylinder, and the outlet of the dust collection chamber located on an end face of said cylinder. However, in the case of 5 sander 301, the dust collection chamber is oriented with its longitudinal axis substantially perpendicular to the axis of the sander, whereas in the case of sander 303, the dust collection chamber is oriented with its longitudinal axis substantially parallel to the axis of the sander. Thus the dust collection chamber of sander 301 vents sideways to atmospheric air, whereas the dust collection chamber of sander 10 303 vents to atmospheric air in a forward direction with respect to the orientation of the sander. It may also be seen from Fig. 10 that although the dust collection chambers of sanders 301 and 303 are substantially cylindrical in shape, they are not exactly so, 15 and are instead slightly tapered in a direction away from the end face of the chamber where the outlet thereof is located. This is for aesthetic and/or ergonomic reasons and does not affect the efficiency of the dust extraction achieved with these embodiments. 20 Sander 302 shown in Fig. 10 is instead provided with a dust collection chamber substantially in the shape of a drum having an axis of rotational symmetry oriented substantially vertically with respect to sander 302, the inlet to said dust collection chamber being located on the curved surface of said drum, and the outlet of said dust collection chamber being located on the upper face of said drum. Thus the dust 25 collection chamber of sander 302 vents to atmospheric air in a vertical direction. Fig. 11 is a perspective view of quarter-sheet sander 301. As may be seen from Fig. 11, the dust collection chamber 50 contains a second smaller cylinder 56, which has the same orientation as and is coaxial with the outer wall of the dust 30 collection chamber, and is open at one end 58 thereof to the interior of the dust collection chamber and at the other end thereof provides the outlet from the dust collection chamber. The filter 60 is located around said outlet. P-AU-CS1217 14 Fig 12A is a partially cut-away view of sander 301 seen from one side thereof and showing airflow within the dust extraction system during operation of sander 301. Dust-laden air is drawn by fan 70 from a point of contact between a sheet of sandpaper held by the platten 32 of the sander and a workpiece through holes 321, 5 322 formed in the platten, and passes up through duct 40 into dust collection chamber 50. Here, the air circulates around second smaller cylinder 56, before leaving the dust collection chamber 50 through outlet 54. Fig. 12B is a partially cut-away view of sander 301 seen from the rear thereof, which shows the airflow within the dust collection chamber 50 more clearly. Dust 10 laden air entering the dust collection chamber through inlet 52 swirls around the second smaller cylinder 56 within chamber 50 and is deposited in the bottom thereof. Inlet 52 is located well above a horizontal plane having at least two-thirds of the interior volume of the dust collection chamber above that plane, so that when fan 70 is switched off, the dust is unable to return back down duct 40 under the action of 15 gravity. Finally, air is exhausted from the dust collection chamber through outlet 54 located in the middle of the chamber and passes through filter 60 which is located around said outlet. Fig. 13 is a perspective view of random-orbit sander 302. As may be seen from 20 Fig. 13, the duct 40 connecting the working head of the sander with the dust collection chamber 50 is contained within a handle 38 of the sander. Dust collection chamber 50 further comprises a filter cleaning lever 58 for agitating filter 60 contained therein. When lever 58 is moved by a user in a circumferential direction, a tongue attached to level 58 knocks against pleats formed in the filter 60, thereby 25 dislodging dust blocking the filter and causing it to fall down into the dust collection chamber. Fig. 14 is a partially cut-away view of sander 302 seen from one side thereof and shows airflow within its dust extraction system during operation of sander 302. 30 Dust-laden air is drawn by fan 70 from a point of contact between a sheet of sandpaper held by platten 32 and a workpiece through holes 321, 322 formed in the platten, and passes up through duct 40 into the inlet 52 of dust collection chamber 50. Dust collection chamber 50 is formed substantially in the shape of a drum having an axis of rotational symmetry oriented substantially vertically with respect to sander P-AU-CS1217 15 302, with the inlet 52 to the dust collection chamber located on the curved surface of the drum, and the outlet 54 thereof located on the upper face of said drum. Dust collection chamber 50 contains a pleated filter having a generally cylindrical shape and which comprises a pleated filter element 601 shaped into the curved surface of a 5 cylinder and a blank wall 602 which forms one of the end faces of said cylinder. The other end face thereof is open to the outlet 54 of the dust collection chamber 50. Hence, dust-laden air entering dust collection chamber 50 through inlet 52 swirls around the filter within chamber 50 and the dust is deposited in the bottom thereof, before the air passes through filter element 601 and is exhausted to atmospheric air 10 through outlet 54. It can also be seen from Fig. 14 that dust collection chamber 50 comprises a lid 501 and a body portion 502, which allows the dust collection chamber 50 to be opened by a user and emptied. As may be seen in Fig. 13, body portion 502 is 15 transparent, allowing a user to see the level of dust collected in the chamber and therefore when it needs emptying. Fig. 15 is a perspective view of belt sander 303, showing dust collection chamber 50 to advantage. As can be seen in Fig. 15, outlet 54 of dust collection 20 chamber 50 reveals a pleated filter 60. Fig. 16 is a partially cut-away view of sander 303 seen from one side thereof and shows airflow within its dust extraction system during operation of sander 303. As may be seen from Fig. 16, duct 40 comprises a first length 401 thereof connecting 25 the region where dust is generated by the sander with a chamber housing fan 70 and a second length 402 thereof connecting the fan chamber with the inlet 52 of the dust collection chamber 50. Filter 60 contained within dust collection chamber 50 has the shape of a truncated cone (or frustrum). Thus dust laden air is drawn firstly up length 401 of duct 40 into the chamber of fan 70 and thence through the second length 402 30 of duct 40 into dust collection chamber 50, where it swirls around filter 60 and the dust is deposited in the bottom of chamber 50, before the air passes through the pleated filter 60 and is exhausted to atmospheric air through outlet 54. Once again, dust collection chamber 50 comprises a lid 501 and a body portion 502, which allows the dust collection chamber 50 to be opened by a user and emptied. As may also be P-AU-CS]217 16 seen from Fig. 15, body portion 502 is transparent, allowing a user to see the level of dust collected in the chamber and therefore when it needs emptying. Throughout this specification and the claims which follow, unless the context 5 requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 10 The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia. 15 P-AU.CS1217

Claims

1. A power tool comprising: a working head for holding a working element; a duct having an inlet locatable in proximity to a point of contact between the working element and a workpiece; 5 a dust collection chamber having an inlet in fluid communication with an outlet from said duct, and an outlet in fluid communication with atmospheric air; a fan operable to transport air from the inlet of said duct to the outlet thereof; and a filter located in fluid flow between the outlet of said dust collection chamber 10 and atmospheric air; wherein the dust collection chamber has a substantially circular cross section, the inlet to said dust collection chamber is at the perimeter of said circle and the outlet of said dust collection chamber is from the middle of said circle. 15

2. A power tool according to claim 1, wherein the cross-sectional area of the inlet to the dust collection chamber is greater than or equal to the cross-sectional area of the inlet to the duct.

3. A power tool according to claim 1 or claim 2, wherein the cross-sectional area 20 of the outlet from the dust collection chamber is greater than or equal to the cross sectional area of the inlet thereto.

4. A power tool according to any one of claims 1 to 3, wherein the cross-sectional area of the outlet from the dust collection chamber is greater than or equal to the 25 cross-sectional area of the inlet to the duct.

5. A power tool according to any one of the preceding claims, wherein the inlet to the dust collection chamber is located above a horizontal plane having at least two thirds of the interior volume of the dust collection chamber above the plane. 30

6. A power tool according to any one of the preceding claims, wherein the exterior of the dust collection chamber is substantially symmetrical about a vertical plane P-AU-CS1217 18 containing the longitudinal axis of the power tool, such that the power tool is usable by a left- or by a right-handed person.

7. A power tool according to any one of the preceding claims, wherein the dust 5 collection chamber is detachable from the power tool, the outlet of the duct and the inlet to the dust collection chamber have complementary asymmetric profiles, and the dust collection chamber is attachable to the outlet of the duct in only one possible configuration. 10

8. A power tool according to any one of claims 1 to 5, wherein the exterior of the dust collection chamber is asymmetric about a vertical plane containing the longitudinal axis of the power tool, the dust collection chamber is detachable from the power tool, and the dust collection chamber is attachable to the outlet of the duct in two possible alternative configurations, one configuration being for use of the power 15 tool by a left-handed person, and the other configuration being for use of the power tool by a right-handed person.

9. A power tool according to any one of the preceding claims, wherein the duct is contained within a handle of the power tool. 20

10. A power tool according to any one of the preceding claims, wherein the dust collection chamber is provided with an anti-static or conductive coating, or with an earthing wire. 25

11. A power tool according to any one of the preceding claims, wherein the dust collection chamber is at least partially transparent.

12. A power tool according to claim 11, wherein the transparent parts of the dust collection chamber are made of polypropylene. 30

13. A power tool according to any one of the preceding claims, wherein the dust collection chamber is at least partially made of glass-filled nylon. P-AU-CS 1217 19

14. A power tool according to any one of the preceding claims, wherein the dust collection chamber comprises a door or lid.

15. A power tool according to one of the preceding claims, wherein the filter is 5 removable from the dust collection chamber and replaceable.

16. A power tool according to any one of the preceding claims, wherein the filter is one of a fabric filter, a pleated filter or a mesh. 10

17. A power tool according to any one of the preceding claims, wherein the filter comprises a first filter element for filtering course dust and a second filter element for filtering finer dust than the first filter element.

18. A power tool according to any one of the preceding claims, wherein the dust 15 collection chamber is substantially in the shape of a cylinder having a longitudinal axis oriented substantially horizontally with respect to the power tool, the inlet to said dust collection chamber is located on the curved surface of said cylinder, and the outlet of said dust collection chamber is located on an end face of said cylinder. 20

19. A power tool according to any one of the preceding claims, wherein the dust collection chamber is substantially in the shape of a drum having an axis of rotational symmetry oriented substantially vertically with respect to the power tool, the inlet to said dust collection chamber is located on the curved surface of said drum, and the outlet of said dust collection chamber is located on the upper face of said drum. 25

20. A power tool according to claim 18 or claim 19, wherein the filter is located centrally within the dust collection chamber coaxially with said axis of the dust collection chamber. 30

21. A power tool according to claim 18, wherein the dust collection chamber contains a second smaller cylinder, the second smaller cylinder has the same orientation as and is coaxial with the first said cylinder, the second cylinder is open at one end thereof to the interior of the dust collection chamber and at the other end P-AU-CS1212 20 thereof provides the outlet from the dust collection chamber, and the filter is located across or around said outlet.

22. A power tool according to claim 19, wherein the dust collection chamber 5 contains a second smaller drum, the second smaller drum has the same orientation as and is coaxial with the first said drum, the second drum is open on the lower face thereof to the interior of the dust collection chamber and on the upper face thereof provides the outlet from the dust collection chamber, and the filter is located across or around said outlet. 10

23. A power tool according to any one of the preceding claims, wherein the fan is located on a drive shaft of a motor of the power tool, which motor also provides the motive power for the working head of the power tool. 15

24. A power tool according to claim 23, wherein the drive shaft carries a second fan operable to cool said motor, said second fan being contained in a chamber of said power tool which is sealed from fluid communication with said duct.

25. A dust extraction module for use with a power tool, said dust extraction module 20 comprising: a dust collection chamber having an inlet connectable in fluid communication with an outlet of a dust-extracting duct of said power tool, and having an outlet in fluid communication with atmospheric air; and a filter locatable in fluid flow between the outlet of said dust collection chamber 25 and said atmospheric air; wherein the dust collection chamber has a substantially circular cross section, the inlet to said dust collection chamber is at the perimeter of said circle and the outlet of said dust collection chamber is from the middle of said circle. 30

26. A dust extraction module according to claim 25, wherein the cross-sectional area of the outlet from the dust collection chamber is greater than or equal to the cross-sectional area of the inlet thereto. 21

27. A dust extraction module according to claim 25 or claim 26, wherein the inlet to the dust collection chamber is located above a horizontal plane having at least two thirds of the interior volume of the dust collection chamber above the plane. 5

28. A dust extraction module according to any one of claims 25 to 27, wherein the inlet to the dust collection chamber has an asymmetric profile or has a profile with rotational symmetry of 180 degrees.

29. A dust extraction module according to any one of claims 25 to 28, wherein the 10 dust collection chamber is provided with an anti-static or conductive coating, or with a connector to an earthing wire.

30. A dust extraction module according to any one of claims 25 to 29, wherein the dust collection chamber is at least partially transparent. 15

31. A dust extraction module according to claim 30, wherein the transparent parts of the dust collection chamber are made of polypropylene.

32. A dust extraction module according to any one of claims 25 to 31, wherein the 20 dust collection chamber is at least partially made of glass-filled nylon.

33. A dust extraction module according to any one of claims 25 to 32, wherein the dust collection chamber comprises a door or lid. 25

34. A dust extraction module according to any one of claims 25 to 33, wherein the filter is removable from the dust collection chamber and replaceable.

35. A dust extraction module according to any one of claims 25 to 34, wherein the filter is one of a fabric filter, a pleated filter or a mesh. 30

36. A dust extraction module according to any one of claims 25 to 35, wherein the filter comprises a first filter element for filtering course dust and a second filter element for filtering finer dust than the first filter element. 22

37. A dust extraction module according to any one of claims 25 to 36, wherein the dust collection chamber is substantially in the shape of a cylinder having a longitudinal axis, the inlet to said dust collection chamber is located on the curved surface of said cylinder, and the outlet of said dust collection chamber is located on 5 an end face of said cylinder.

38. A dust extraction module according to any one of claims 25 to 37, wherein the dust collection chamber is substantially in the shape of a drum having an axis of rotational symmetry, the inlet to said dust collection chamber is located on the curved 10 surface of said drum, and the outlet of said dust collection chamber is located on a face of said drum.

39. A dust extraction module according to claim 37 or claim 38, wherein the filter is located centrally within the dust collection chamber coaxially with said axis of the 15 dust collection chamber.

40. A dust extraction module according to claim 37, wherein the dust collection chamber contains a second smaller cylinder, the second smaller cylinder has the same orientation as and is coaxial with the first said cylinder, the second cylinder is 20 open at one end thereof to the interior of the dust collection chamber and at the other end thereof provides the outlet from the dust collection chamber, and the filter is located across or around said outlet.

41. A dust extraction module according to claim 38, wherein the dust collection 25 chamber contains a second smaller drum, the second smaller drum has the same orientation as and is coaxial with the first said drum, the second drum is open on one face thereof to the interior of the dust collection chamber and on the other face thereof provides the outlet from the dust collection chamber, and the filter is located across or around said outlet. 30

42. A power tool substantially as hereinbefore described with reference to the accompanying drawings. 23

43. A dust extraction module substantially as hereinbefore described with reference to the accompanying drawings.